This invention relates generally to a piston engaged inside a cylindrical container, which serves as a movable bottom of the container and functions for enhancing fluidtightness inside the container.
As a piston for enhancing airtightness inside a cylinder, Japanese Patent Laid-open No. 1996-280804 discloses a piston for a syringe, for example. However, a cylinder produced by injection molding, for example, often has a tapered inner wall for production process convenience, and in that case, the conventional piston could not maintain fluidtightness because an internal diameter of the cylinder changes whereas the diameter of the piston does not significantly change. Further, the conventional piston is normally designed for short term use, and the seal between the piston and the inner wall tends to be degraded with time.